DC/DC converters are commonly used in electronics today for changing the voltage or the polarity of the feeding electric power. The simplest converter is a linear converter comprising one or several resistors in series with the DC source, dividing the voltage over the resistors. A common type of switched DC/DC converters applies a DC voltage across an inductor with a certain frequency. Typical frequencies are around 100-500 kHz. When the voltage is applied over the inductor, current flows through the inductor and electromagnetic energy is stored in the inductor. When the voltage across the inductor is cut off, the energy stored in the inductor will flow through the load connected to the output of the DC/DC converter. Ideally the input voltage to the DC/DC converter Vin relates to the output voltage of the converter Vout as the total cycle time T relates to the time voltage is applied across the inductor ton, i.e.
            V      in              V      out        =      T          t      on      
By varying the on/off time of voltage over the inductor the output voltage of the DC/DC converter can be varied. This relation is valid for so called step down converters where the output voltage is decreased in relation to the input voltage.
There are also DC/DC converters available that can increase the output voltage in relation to the input voltage or that can change the polarity. Some examples of converter types are Buck, Boost, Buck-boost, Flyback, Push-pull and Sepic. They are all based on the principle of storing energy over an inductor during a first cycle and then releasing the energy during a second cycle. A transistor is used for switching the current flow to the inductor on and off. To do this work the transistor needs a switching voltage applied to its base or gate terminal. This switching voltage is supplied by a gate driver circuit as will be explained below.
FIG. 1a shows a prior art DC/DC converter 100 with two transistors T1 and T2, 101 and 102, connected in series between a ground 103 and a voltage input 104 of the DC/DC converter with a potential Vin. Each transistor has three terminals, gate, source and drain. The gate terminals 105 and 106 of the transistors are connected to a first connection point 107. The source terminal 108 of the transistor T2, 102, is connected to the ground 103. The drain terminal 109 of the transistor T2 is connected to the source terminal 111 of the transistor T1, 101, via a first connection line 110 and the drain terminal 112 of the transistor T1 is connected to the input voltage Vin at the voltage input 104. A first diode 113 is connected between the ground and a second connection point 118. The second connection point 118 is connected to the drain terminal 109 of the transistor T2 via a second connection line 119. Forward direction of the diode is from the ground to the second connection point 118. A first inductor is 114 is connected between the second connection point 118 and a third connection point 115. Finally a first capacitor 116 and a first load 117 are connected in parallel between the ground and the third connection point 115. An output voltage Vout is thus supplied across the load 117. The transistor T1 is of type P-channel enhancement mode and the transistor T2 of a type called N-channel depletion mode. The characteristics of these transistor types are shown in the diagram of FIG. 1b with gate voltage Vg on a horizontal axis 123 and drain current Id on a vertical axis 124. The drain current through the transistor T1 is shown with a curve 121 and the corresponding current through the transistor T2 is shown with a curve 122. As can be seen the current through the transistor T1 increases with decreased gate voltage while current through the transistor T2 increases with increased gate voltage. These transistors are therefore called complementary transistors. The gate voltage Vg at which the drain current Id is zero is called the pinch-off voltage. The first connection point 107 is fed by a square wave pulse varying between 0V and a negative voltage supplied by a pulse generator 130 via a first resistor 131 being an inner resistance of the pulse generator 130. At negative input voltage the transistor T2 will be switched off and the transistor T1 will be switched on, current will in this first phase flow through the transistor T1, the second connection point 118 will assume a potential close to Vin and causing current to flow through the first inductor 114 and the first load 117. At 0V input voltage the transistor T1 will be switched off and the transistor T2 will be switched on causing the second connection point 118 to assume a value close to ground potential. In this second phase electromagnetic energy stored in the first inductor during the first phase will cause current to flow through the first load and the first diode. This second phase is also called the freewheel phase.
Another prior art solution for a DC/DC converter 200 is shown in FIG. 2 using a transformer, making it possible to use only one transistor. The transformer 201 has a primary winding 202 and a secondary winding 203. The primary winding is fed by a square wave pulse varying between 0V and a negative voltage supplied by a pulse generator 204 via a second resistor 205 being the inner resistance of the pulse generator 204. The secondary winding 203 having two ends, the first end is connected to a source terminal 206 and the second end to a gate terminal 207 of a transistor T3, 208. Drain terminal 209 of the transistor T3 is connected to an input voltage Vin at a point 210. A second diode 211 is connected between a ground 214 and the source terminal 206 with forward direction from the ground 214 to the source terminal 206. A second inductor 212 is connected between the source terminal 206 and a fourth connection point 213. Finally a second capacitor 215 and a second load 216 are connected in parallel between the ground 214 and the fourth connection point 213. The transistor T3 is of P-channel enhancement type or N-channel depletion type. The varying gate voltage will cause the transistor T3 to be switched on and off which means that the source terminal will assume a positive voltage Vin and a negative voltage. When the transistor T3 is switched on current will flow through the second inductor 212 and the second load 216. When the transistor T3 is switched off electromagnetic energy stored in the second inductor 212 during the phase when the transistor is switched on will cause current to flow through the second load and the second diode. This is also called the freewheel phase.
In both prior art solutions described above the switch transistors T1, T2 and T3 in the DC/DC converters are switched on and off by a switching voltage provided by a pulse generator including also a transformer in the example of FIG. 2. Henceforth in the description a gate driver is defined as a circuit providing a switching voltage to the DC/DC converter causing the switching transistor or transistors in the DC/DC converter to be switched on and off. In the example of FIG. 1 the gate driver comprises the pulse generator and in the example of FIG. 2 the gate driver comprises the pulse generator and the transformer.
In many applications today there is a need for DC/DC converters having high switching frequencies at high voltages and being able to supply high power with good thermal efficiency. The Monolithic Microwave Integrated Circuit (MMIC) technology is well suited to meet these requirements. However also RFIC (Radio Frequency Integrated Circuit) can be used even if this process can not be used at as high frequencies as MMIC. In many applications where an RF-amplifier is made in an MMIC chip or RFIC chip it would be desirable to integrate also a DC/DC converter and gate driver in the same chip.
However gate drivers of today are made of discrete components and DC/DC converters are often based on using complementary transistors and/or transformers not allowing integration in MMIC or RFIC. These solutions are also space consuming and relatively slow.
US 2005/0242795 A1 discloses an MMIC DC/DC converter fabricated in GaAs technology. A drawback with this solution is that it does not allow a high power output.
Thus there is a need for an improved alternative solution for a compact and fast gate driver circuit and DC/DC converter possible to integrate in MMIC or RFIC and allowing at the same time a high output power from the DC/DC converter where the transistors are realized in an MMIC or an RFIC manufacturing process. There is also a need for a power converter comprising the gate driver circuit and the DC/DC converter.